1. Field of the Invention
The present invention relates to an autonomously movable legged mobile robot apparatus and a walking control method of the robot apparatus. More particularly, the present invention relates to a robot apparatus and its walking control method capable of locomotion on such areas as floors whose surface states for walking greatly vary.
This application claims priority of Japanese Patent Application No. 2003-329131, filed on Sep. 19, 2003, the entirety of which is incorporated by reference herein.
2. Description of the Related Art
A term “robot” refers to a mechanical apparatus that simulates motions of human beings (creatures) by using electric or magnetic actions. In Japan, robots began to spread at the end of 1960s. Many of them were industrial robots such as manipulators and transfer robots for automating and unmanned manufacturing works in factories.
Recently, practical robots are being developed as partners of human beings to assist in their life, i.e., human activities for living conditions and the other various situations in daily life. Unlike the industrial robots, the practical robots have capabilities to self-learn the method of adaptation to human beings having different individual characteristics or to diverse environments in various aspects of living environments for human beings. For example, robot apparatuses that are already put to practical use include “pet-type” robots and “human-type” or “human-like” robots (humanoid robots). The pet-type robots simulate the body mechanism and motions of quadrupedal walking animals such as dogs and cats. The humanoid robots are designed and modeled on the body mechanism and motions of bipedal upright walking human beings and the like.
Compared to industrial robots, the practical robots also referred to as entertainment robots because they are capable of various entertainment-oriented motions, for example. Such robot apparatuses are equipped with imaging means such as cameras and various sensors to obtain information from the outside and can autonomously behave in accordance with the external information (external stimulus) and internal states of the robots themselves.
These robot apparatuses include legged mobile ones such as bipedal walking robot apparatuses. It is particularly difficult for a bipedal walking robot apparatus to walk on a floor surface having, e.g., slopes and obstructions by balancing the whole body under actual environments. Normally, robot walking is made possible by computing control signals to be output to an actuator provided for each joint based on floor reaction forces, joint angles, and the like obtained from sensors and the like provided for foot soles.
For example, patent document 1: Japanese Patent Application Laid-Open No. 2001-328083 discloses the technology of a floor shape estimation apparatus for a legged mobile robot apparatus that walks by simultaneously estimating a landing surface inclination for a foot and a height difference between landing surfaces for both feet.
The technology described in the above-mentioned patent document 1 enables smooth walking by estimating local shapes of the floor surface. However, there is provided no information about the floor surface until the feet actually touch the floor. Such scheme simply modifies a very short walking schedule.
That is to say, it is possible to adaptively compute correction amounts (adaptive operation amounts) of trajectories each time the feet touch the floor surface. However, it is impossible to obtain knowledge about the floor surface at every step before the foot touches the floor. Further, it is impossible to automatically discriminate an optimal control mode for the floor surface by supposing not the step-based area but the larger area (of the floor surface) during the walking control. An adaptive operation amount needs to be computed based on predetermined control modes. The adaptive operation amount in the above-mentioned patent document 1 and the like signifies a correction amount corresponding to floor surface's inclinations and robot's attitudes against a walking control model defined as a given reference. Accordingly, it is possible to continuously or slowly change the control contents of the walking control model. There occurs a problem of making the walking difficult in cases that cannot be solved by such adaptive operation only.
For example, the robot apparatus may walk on hard landing surfaces (floor surfaces) such as flooring, marble stone, and concrete or on soft landing surfaces such as carpets and lawn. In these cases, there are used completely different parameters, coefficients, or walking algorithms (walking models) for computing adaptive operation amounts corresponding to the current floor surface, for example, from a walking control model as the walking control mode used as the reference. Without changing the walking control mode, simply computing the adaptive operation amount cannot allow locomotion between greatly varying floor surface states, for example, from the hard landing surface to the soft landing surface. During such locomotion, the robot apparatus itself cannot even discriminate whether or not the walking is possible. An operator needs to manually reconfigure knowledge about the floor surface. Specifically, it has been necessary to reconfigure parameters for computing adaptive operation amounts corresponding to the floor surface, for example.